In the recording method using an inkjet printer which is one of the typical methods among various color recording methods, various methods for discharging ink have been developed, and in any of them, ink droplets are generated and adhered onto various record-receiving materials (such as paper, film and cloth) to perform recording. This has been rapidly prevailing lately and is expected to continue growing remarkably in the future because of features such as quietness without noise generation due to no contact of a recording head with a record-receiving material and as easiness in downsizing, speeding up and colorizing.
Conventionally, as an ink for fountain pens, felt-tip pens or the like and as an ink for inkjet recording, water-based inks where a water-soluble dye is dissolved in an aqueous medium have been used. To these water-based inks, a water-soluble organic solvent is generally added in order to prevent ink from clogging at a pen tip or an inkjet nozzle. These conventional inks are required to provide recorded images with sufficient density, not to clog at a pen tip or a nozzle, to dry quickly on a record-receiving material, to bleed less, to have an excellent storage stability, and so on. In addition, formed images are required to have fastnesses such as water fastness, light fastness and moisture fastness.
Meanwhile, images or character information on color displays of computers are generally expressed by subtractive color mixing of 4 color inks of yellow (Y), magenta (M), cyan (C) and black (K), for color recording by an ink jet printer. In order that images expressed by additive color mixing of red (R), green (G) and blue (B) on CRT displays and the like is reproduced, as faithfully as possible, with images expressed by subtractive color mixing, it is desired that each of Y, M and C has a hue as close to each standard as possible and is also vivid. In addition, it is required that ink compositions are stable in storage for a long period of time, and that images printed therewith have a high concentration and also said images are excellent in fastnesses such as water fastness, light fastness, and gas fastness.
The application of inkjet printers has been widely spread in the fields ranging from small printers for office automation to large printers for industrial use, and therefore fastnesses such as water fastness, moisture fastness, light fastness and gas fastness have been required more than ever.
Water fastness has been largely improved by coating a paper surface with inorganic particles which can absorb the coloring matter in an ink, such as porous silica, cation polymer, aluminasol, special ceramic and the like, together with a PVA resin.
“Moisture fastness” means durability against a phenomenon that the dye in a record-receiving material bleeds during storage of the colored record-receiving material under an atmosphere of high humidity. Dye bleeding extremely deteriorates image quality of images particularly required to have a photo-like and high resolution image quality, and therefore it is important to reduce such bleeding as far as possible.
As for light fastness, any technique for large improvement thereof has not established yet. In particular, many of coloring matters for magenta among 4 primary colors of Y, M, C and K originally have low light fastness, and therefore improvement thereof is an important problem. In addition, with recent spread of digital cameras, there are more opportunities to print pictures at home, and image discoloration by oxidizing gas in the air where printed matters obtained are stored is acknowledged as a problem. The oxidizing gas reacts with dyes on or in a recorded paper, causing discoloration or fading of the printed image. Among oxidizing gasses, ozone gas is regarded as a causative agent accelerating color-fading phenomenon of inkjet-recorded images. This phenomenon of discoloration or fading is characteristic of inkjet images, and therefore improvement of ozone gas fastness is also an important problem.
As a magenta coloring matter used in water-based inks for inkjet recording, typical are xanthene-based coloring matters and azo based coloring matters using H acid. However, xanthene-based coloring matters are very excellent in hue and vividness but very inferior in light fastness. On the other hand, some of the azo-based coloring matters using H acid are good in terms of hue and water fastness, but many are inferior in light fastness, gas fastness and vividness. As for this type, a magenta dye excellent in vividness and light fastness has been developed but it still has a low level in light fastness compared with dyes having a different hue such as a cyan dye represented by a copper phthalocyanine-based coloring matter and a yellow dye.
Examples of the magenta coloring matter excellent in vividness and light fastness include an anthrapyridone-based coloring matter (see, for example, Patent Literatures 1 to 12), but a coloring matter for magenta satisfying all the requirements for hue, vividness, light fastness, water fastness, gas fastness and solution stability has yet to be obtained.
In particular, Patent Literatures 9 and 12 disclose a compound having a structure of cross-linking two molecules of anthrapyridone compounds with a cross-linking group, and an ink composition containing said compounds.    Patent Literature 1: JP H10-306221 A (pp. 1 to 3 and 7 to 18)    Patent Literature 2: JP 2000-109464 A (pp. 1 to 2 and 8 to 12)    Patent Literature 3: JP 2000-169776 A (pp. 1 to 2 and 6 to 9)    Patent Literature 4: JP 2000-191660 A (pp. 1 to 3 and 11 to 14)    Patent Literature 5: JP 2000-256587 A (pp. 1 to 3 and 7 to 18)    Patent Literature 6: JP 2001-72884 A (pp. 1 to 2 and 8 to 11)    Patent Literature 7: JP 2001-139836 A (pp. 1 to 2 and 7 to 12)    Patent Literature 8: WO 2004/104108 (pp. 20 to 36)    Patent Literature 9: JP 2003-192930 A (pp. 1 to 4 and 15 to 18)    Patent Literature 10: JP 2005-8868 A (pp. 1 to 3 and 15 to 22)    Patent Literature 11: JP 2005-314514 A (pp. 1 to 3 and 15 to 20)    Patent Literature 12: WO 2006/075706